Well let's see.. here's a question I have:
Is there anywhere in the deal that they tell you the propane from that 200gal tank can ONLY be used in the tanks for the mowers and other equipment?
Propane for a bottle refill right now is running about $3.89 here in the central Texas area, 87 octane gas at Wal-Mart is/was $3.22 gallon today. Now, which gas pricing are they using in your area, a daily reported average cost or a national average?
I've heard reports of propane up north going for $7.00/gallon or more right now with the winter we're having. If you aren't limited to using it JUST in your mowers and all of the other questions I raised work out, then I would say go for it. I'd also look into converting anything else you can to propane also.. say a small vehicle or two?